From: Stephen Hemminger <stephen@networkplumber.org> Date: 2018-03-12 18:46:01
Since indirect calls are expensive, and now even more so, perhaps we should figure out
a way to make the default TCP congestion control hooks into direct calls.
99% of the users just use the single CC module compiled into the kernel.
Use some macros (or other stuff) to change indirect call to direct
calls. So that code like:
static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
to:
static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
const struct tcp_congestion_ops *ops = inet_csk(sk)->icsk_ca_ops;
if (ops == default_tcp_ops)
default_tcp_cong_avoid(s, ack, acked);
else
icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
The use macros and/or compiler symbols so the builtin (non-module) congestion
control is always default_tcp_XXX.
From: David Miller <davem@davemloft.net> Date: 2018-03-12 19:04:08
From: Stephen Hemminger <stephen@networkplumber.org>
Date: Mon, 12 Mar 2018 11:45:52 -0700
Since indirect calls are expensive, and now even more so, perhaps we should figure out
a way to make the default TCP congestion control hooks into direct calls.
99% of the users just use the single CC module compiled into the kernel.
Who is this magic user with only one CC algorithm enabled in their
kernel? I want to know who this dude is?
I don't think it's going to help much since people will have I think
at least two algorithms compiled into nearly everyone's tree.
Distributions will enable everything.
Google is going to have at least two algorithms enabled.
etc. etc. etc.
Getting rid of indirect calls is a fine goal, but the precondition you
are mentioning to achieve this doesn't seem practical at all.
From: Stephen Hemminger <stephen@networkplumber.org> Date: 2018-03-12 19:48:16
On Mon, 12 Mar 2018 15:04:06 -0400 (EDT)
David Miller [off-list ref] wrote:
From: Stephen Hemminger <stephen@networkplumber.org>
Date: Mon, 12 Mar 2018 11:45:52 -0700
quoted
Since indirect calls are expensive, and now even more so, perhaps we should figure out
a way to make the default TCP congestion control hooks into direct calls.
99% of the users just use the single CC module compiled into the kernel.
Who is this magic user with only one CC algorithm enabled in their
kernel? I want to know who this dude is?
I don't think it's going to help much since people will have I think
at least two algorithms compiled into nearly everyone's tree.
Distributions will enable everything.
Google is going to have at least two algorithms enabled.
etc. etc. etc.
Getting rid of indirect calls is a fine goal, but the precondition you
are mentioning to achieve this doesn't seem practical at all.
What I meant is that kernels with N congestion controls, almost all traffic
uses the default So that path can be optimized. The example I gave would
have all the others doing the same indirect call.
From: Eric Dumazet <hidden> Date: 2018-03-12 20:03:38
On 03/12/2018 12:48 PM, Stephen Hemminger wrote:
On Mon, 12 Mar 2018 15:04:06 -0400 (EDT)
David Miller [off-list ref] wrote:
quoted
From: Stephen Hemminger <stephen@networkplumber.org>
Date: Mon, 12 Mar 2018 11:45:52 -0700
quoted
Since indirect calls are expensive, and now even more so, perhaps we should figure out
a way to make the default TCP congestion control hooks into direct calls.
99% of the users just use the single CC module compiled into the kernel.
Who is this magic user with only one CC algorithm enabled in their
kernel? I want to know who this dude is?
I don't think it's going to help much since people will have I think
at least two algorithms compiled into nearly everyone's tree.
Distributions will enable everything.
Google is going to have at least two algorithms enabled.
etc. etc. etc.
Getting rid of indirect calls is a fine goal, but the precondition you
are mentioning to achieve this doesn't seem practical at all.
What I meant is that kernels with N congestion controls, almost all traffic
uses the default So that path can be optimized. The example I gave would
have all the others doing the same indirect call.
I do not understand. What is default_tcp_ops anyway ?
How changes to /proc/sys/net/ipv4/tcp_congestion_control will impact this ?
From: David Miller <davem@davemloft.net> Date: 2018-03-12 20:05:18
From: Eric Dumazet <redacted>
Date: Mon, 12 Mar 2018 13:03:35 -0700
On 03/12/2018 12:48 PM, Stephen Hemminger wrote:
quoted
On Mon, 12 Mar 2018 15:04:06 -0400 (EDT)
David Miller [off-list ref] wrote:
quoted
From: Stephen Hemminger <stephen@networkplumber.org>
Date: Mon, 12 Mar 2018 11:45:52 -0700
quoted
Since indirect calls are expensive, and now even more so, perhaps we
should figure out
a way to make the default TCP congestion control hooks into direct
calls.
99% of the users just use the single CC module compiled into the
kernel.
Who is this magic user with only one CC algorithm enabled in their
kernel? I want to know who this dude is?
I don't think it's going to help much since people will have I think
at least two algorithms compiled into nearly everyone's tree.
Distributions will enable everything.
Google is going to have at least two algorithms enabled.
etc. etc. etc.
Getting rid of indirect calls is a fine goal, but the precondition you
are mentioning to achieve this doesn't seem practical at all.
What I meant is that kernels with N congestion controls, almost all
traffic
uses the default So that path can be optimized. The example I gave
would
have all the others doing the same indirect call.
I do not understand. What is default_tcp_ops anyway ?
How changes to /proc/sys/net/ipv4/tcp_congestion_control will impact
this ?
I'm also confused what is being suggested exactly and how this can
work. :-)
From: Stephen Hemminger <stephen@networkplumber.org> Date: 2018-03-12 20:51:26
On Mon, 12 Mar 2018 16:05:16 -0400 (EDT)
David Miller [off-list ref] wrote:
From: Eric Dumazet <redacted>
Date: Mon, 12 Mar 2018 13:03:35 -0700
quoted
On 03/12/2018 12:48 PM, Stephen Hemminger wrote:
quoted
On Mon, 12 Mar 2018 15:04:06 -0400 (EDT)
David Miller [off-list ref] wrote:
quoted
From: Stephen Hemminger <stephen@networkplumber.org>
Date: Mon, 12 Mar 2018 11:45:52 -0700
quoted
Since indirect calls are expensive, and now even more so, perhaps we
should figure out
a way to make the default TCP congestion control hooks into direct
calls.
99% of the users just use the single CC module compiled into the
kernel.
Who is this magic user with only one CC algorithm enabled in their
kernel? I want to know who this dude is?
I don't think it's going to help much since people will have I think
at least two algorithms compiled into nearly everyone's tree.
Distributions will enable everything.
Google is going to have at least two algorithms enabled.
etc. etc. etc.
Getting rid of indirect calls is a fine goal, but the precondition you
are mentioning to achieve this doesn't seem practical at all.
What I meant is that kernels with N congestion controls, almost all
traffic
uses the default So that path can be optimized. The example I gave
would
have all the others doing the same indirect call.
I do not understand. What is default_tcp_ops anyway ?
How changes to /proc/sys/net/ipv4/tcp_congestion_control will impact
this ?
I'm also confused what is being suggested exactly and how this can
work. :-)
Trying to directly call the fastpath TCP congestion operations for sockets
using the default. The problem is how to do this and it gets messy with Kconfig
and CPP to deal with as raw tools. Maybe weak symbols could be used.